1. Field of the Invention
The present invention relates to an engine with a variable combustion chamber which can be modified into a direct-injection-type combustion chamber when the engine operates under low load and a prechamber-type combustion chamber when the engine operates under high load, and more particularly to such an engine which employs alcohol as fuel.
2. Prior Art
Fuel for use in conventional engines is fossil fuel such as gasoline, light oil, or the like. The fossil fuel is a limited natural resource. Exhaust gases emitted from engines which burn gasoline, light oil, etc. contain harmful substances which are partly responsible for the air pollution. Various efforts have been made to eliminate or reduce these shortcomings. Among the various attempts has been an engine which uses, as fuel, alcohol which is chemically or biochemically produced.
Alcohol has a greater latent heat value of vaporization and generates smaller heat than conventional fuels. For example, in order to produce the same amount of heat, it is necessary to supply an engine with alcohol which is about 1.6 times light oil. Since the amount of alcohol injected into an engine cylinder is larger, air and injected alcohol are not easily mixed together in the combustion chamber, and the time required for the alcohol to be diffused and combusted is longer. Especially when the engine is subjected to high load, the amount of alcohol to be injected is increased and hence the engine output power and the combustion efficiency are lowered.
When alcohol is supplied in an amount which is 1.6 times, then its latent heat of vaporization is about 5.6 times that of light oil. Therefore, alcohol less tends to be vaporized in the combustion chamber. When the engine is started or the temperature of ambient air is low, alcohol is not fully burned, and unburned gases are emitted from the engine, with the results that uncomfortable odors are produced and air is polluted by harmful substances contained in the emitted unburned gases. In addition, the injected alcohol may not be ignited, and the engine may not be started.
Various engines with variable compression ratios have been proposed in order to improve the ability to start at low temperatures. For example, Japanese Utility Model Publication No. 57(1982)-164224 discloses an engine having a main combustion chamber and an auxiliary chamber communicating therewith. In addition to intake and exhaust valves, a third valve is disposed in the opening of the auxiliary chamber. When the engine is under low load, the opening of the auxiliary chamber is closed by the third valve, giving the engine a higher compression ratio. When the engine is under high load, the third valve is opened on each compression stroke, thus reducing the compression ratio for the prevention of knocking. However, the disclosed engine cannot solve the problems referred to above.